Viruses of the family Filoviridae, i.e., filoviruses are pathogens which infect primates including humans to cause serious hemorrhagic fever with an extremely high fatality rate in the infected primates. Mass infection with filoviruses is currently limited to Africa, but there is no denying the possibility that mass infection will also break out in any other regions in the future due to recent advances in the worldwide transportation network. In addition, there is currently no commercially available prophylactic or therapeutic agent which is effective against filovirus infection.
In the family Filoviridae, only two genera, Marburgvirus and Ebolavirus, have been identified. Further, in the genus Ebolavirus, the following five species have been identified: Zaire ebolavirus, Sudan ebolavirus, Tai Forest ebolavirus, Bundibugyo ebolavirus and Reston ebolavirus.
Ebola virus disease (EVD) caused by infection with viruses of the genus Ebolavirus, i.e., ebolaviruses has an average fatality rate of about 50%, and the fatality rate in the past epidemic is in the range of 25% to 90%. The incubation period from infection with ebolaviruses to development of EVD is 2 to 21 days. Early symptoms of EVD are fatigue fever, myalgia, headache and sore throat, which are followed by vomiting, diarrhea, exanthema, renal and hepatic dysfunction, external hemorrhage, and other symptoms.
Recently, studies in monkey infection models have demonstrated that passive immunization with monoclonal antibodies neutralizing ebolavirus infectivity is effective for treatment of EVD (Non-patent Document 1 and Non-patent Document 2). During the epidemic caused in West African in 2014, the infected patients received antibody therapy which had not been approved as a drug. However, monoclonal antibodies hitherto developed exert their effect only on the treatment of EVD caused by Zaire ebolavirus among the five ebolavirus species.
On the other hand, EVD caused by Sudan ebolavirus and Bundibugyo ebolavirus among the five ebolavirus species have also occurred frequently since 2000.